The Vision Research Program Planning Committee of the National Advisory Eye Council has called for research in the diagnosis and treatment of angle-closure glaucoma. We are submitting a proposal that we feel responds to this call. Two approaches to diagnosis will be investigated. The study group will consist of volunteer patients thought to have an increased risk of developing angle-closure glaucoma on the basis of gonioscopy. In the first approach, each patient will be subjected to three angle-closure provocative tests. In the second approach the same patients will undergo measurement of certain biometric parameters: anterior chamber depth, lens thickness, relative position of the lens in the eye, length of the eyeball, and width of the iridocorneal angle (goniometry). The width of the angle will be measured using a newly developed computerized image processing technique. The other parameters will be measured using A-scan ultrasound. These patients will be followed prospectively to see which of them develops angle-closure glaucoma, thus allowing evaluation of the diagnostic value of these tests and measurements. Two therapeutic techniques will be compared on the basis of final visual acuity, visual fields, and slit-lamp appearance of the lens. The volunteer subjects will have positive angle-closure provocative tests and will be assigned randomly to one of two treatment groups. The patients in the first group will undergo prophylactic iridectomy, while those in the second group will simply be observed without medical or surgical therapy. The patients will be followed for three to five years to observe the effects of the treatment.